This invention relates to a component position indicating apparatus, that is to say apparatus which may be used to indicate the position of a component. More particularly, the invention provides apparatus which will indicate whether a first component is in the same position relative to a second component as the position which the first component was in relative to the second component at some historical time. The preferred embodiment of the invention also provides a real time indication as to whether the first component is nearer to or further from the second component than it was at the historical reference time. The preferred embodiment of the invention may accordingly be used as part of the control system for returning the first and second components to the same relative position as they were in at the historical reference time.
There are many instances when it is desirable to bring two components to a position relative to each other which is the same as the position which the components had previously adopted relative to each other. This situation arises whenever the relative position of the two components is first adjusted to produce some particular desired effect, and it is subsequently necessary to re-position the components to produce the same desired effect. One particular example of such a requirement is in the case of inflatable structures where the structure may, at some point, be inflated to produce a particular configuration and in which it is desired subsequently to re-create the same relative position of the components so as to re-produce the same configuration. This requirement may exist, for example, in an inflatable support element of a seat, for example a vehicle seat. In this example a driver may adjust the degree of inflation of an inflatable element (for example an inflatable lumbar support) to optimize comfort of a seat for his personal circumstances. If the vehicle is subsequently not used for some time, and as a result inflation pressure leaks from the lumbar support, it is desirable to have a mechanism which will automatically re-establish the components in to the same relative position as that in which they were in when last adjusted by the driver in question. A similar requirement may exist, for example, in relation to the angle of a seat back relative to a seat cushion. One driver may set this to a particularly desired value and it would be desirable to be able to re-set the angle to that desired value notwithstanding that an occasional user of the seat has altered the angle to suit his particular requirements.
Whilst the particularly preferred embodiments of the invention have been developed for use in connection with vehicle seats, it should be appreciated that the invention is of wide general applicability and may be used in many applications where it is desirable to re-establish the same relative position between two components as was present at some previous historical reference time.
In accordance with one aspect of the present invention a component position indicating apparatus for indicating when a first component is at the same position relative to a second component as it was at some historical reference time, comprising a cable connected to a first component, a sheath which surrounds part of the cable and is connected to the second component whereby relative movement between the first and the second components produces relative movement between the cable and the sheath, a chassis connected to the sheath, a cable drum rotatably mounted in the chassis, the cable being connected to the cable drum with some of the cable wrapped around the cable drum whereby linear movement of the cable relative to the cable sheath causes rotation of the cable drum within the chassis, and sensing means for providing an output characteristic of the position of the cable drum relative to the chassis.
According to one embodiment, a screw-threaded support is mounted on the chassis and the cable drum is screw threadedly mounted on the support whereby rotation of the cable drum results in linear movement of the cable drum relative to the chassis so that movement of the cable relative to the cable sheath causes rotation of the cable drum relative to the screw-threaded support.
Preferably, then, the sensor is a hall effect sensor which is acted upon by a magnet secured to the cable drum.
In use, as the first and second components move relative to each other, the resultant relative movement between the cable and the sheath cause rotation of the cable drum and a change in the linear relative positions of the cable drum and the sensor. The sensor will provide an output characteristic of the linear relative position of the sensor and the cable drum and hence characteristic of the relative positions of the first and second components.
In another preferred embodiment of the invention, the sensing means comprising a potentiometer the resistance of which varies with the angular position of the cable drum relative to the claims, in particular wherein said potentiometer comprises a pair of arcuate contact tracks which are radially spaced apart and which are concentric with the axis of rotation of the cable drum, the cable drum having an electrical contact mounted thereon which engages said contact tracks so as to cause an electrical short therebetween, said electrical contact sweeping along said contact tracks upon rotation of the cable drum so as to vary the position of the short between said tracks and hence to vary their resistance such that each angular position of the cable drum produces a unique resistance across the contact tracks. The contact tracks may be printed on a circuit board mounted on an endcap of the chassis with each contact track preferably subtending an arc about the axis of rotation of the cable drum of substantially 300 degrees.
This arrangement has the advantage that it offers greater accuracy due to the greater resolution which can be delivered with a variable resistor whilst being significantly cheaper than the linear system according to the first embodiment.
In a particularly preferred embodiment of the invention a memory is associated with the sensor so that when the first and second components have been adjusted to a particularly desired position, the memory may record the output of the sensor characteristic of this relative position. The sensor output which has been recorded serves as a datum value for future reference. If at some time in the future it is desired to re-position the first and second components so that they are in the same relative position as they were in at the moment when the sensor output was recorded, it is merely necessary to vary the position of the first and second components until the output of the sensor matches the value recorded in the memory.
Preferably, the characteristics of the sensor are such that the sensor output varies continuously and in the same sense as the first and second components move from one limit of their relative positions to the opposite limit of their relative positions. Accordingly, the sensor output in real time will either be less than or more than the recorded sensor value associated with a particular relative position. Under these circumstances, the output of the sensor may be used as part of a feedback mechanism to control an actuator so that the first and second components may be brought into the same relative position as the components were in when the output of the sensor was recorded.
It will be noted that the apparatus described above offers a number of distinct advantages. Firstly, in many applications no calibration of the apparatus is required. In this respect, the absolute output of the sensor is of no interest. All that the sensor is required to do is to provide an output which is characteristic to the relative positions of the first and second components in the particular assembly of which it forms part. When the first and second components have been brought to their required relative position (for example by running the inflation pump of an inflatable lumbar support), the output of the sensor corresponding to that relative position is recorded. This recorded value may then be used subsequently to re-position the components in the same relative position. Accordingly, all the variations associated with manufacturing tolerances of the components and the assembly thereof are irrelevant to operation of the device. A further advantage of the invention is that it is applicable to determining the relative position of any pair of components which can be connected respectively to a cable and a sheath to provide relative movement between the cable and the sheath as the first and second components move relative to each other. Thus, the invention is applicable to components which move linearly relative to each other and components which move angularly relative to each other.
It will be noted that the entire apparatus may be pre-assembled under factory conditions and supplied as a unit which can be installed merely by connecting the sheath to one of the components and the cable to the other of the components. In this connection, as noted above, no calibration of the device is necessary after the sheath and cable have been secured to their respective components and accordingly the assembly of the pre-formed apparatus and the components whose relative position is to be sensed can be carried out without a requirement for precision assembly techniques.
It should be noted that the term xe2x80x9ccablexe2x80x9d as used herein is intended to mean any flexible material of appropriate mechanical characteristics which may be used to transmit tensile force. The material may be a monofilament material or a woven or laid material and may be of metal or synthetic plastics composition depending on the nature of the components whose relative position is to be indicated.
It should further be noted that although, in the broadest context, the invention is concerned with a device which merely produces an indication of the relative position of two components, the device may be incorporated together with appropriate actuators and feedback arrangements to produce a control system for maintaining the position of one component relative to another at a pre-determined value. For example, the invention could be utilized in association with a pump and appropriate feedback control circuitry to maintain a component supported on an inflatable structure at a predetermined level as the load on the structure varies. This arrangement offers the advantage of offering a particularly effective inflation control system which may be used, for example to control a lumbar support in a vehicle seat. It also has the advantage that it does not require calibration and may also be used to control the maximum inflated position of an air cell, again without requiring a factory calibration of the upper limit on factory set up.
The present invention accordingly further provides an inflation control system comprising an air cell having upper and lower sheets which define a first internal chamber, a second chamber located within and sealed off from said first chamber, the top of said second chamber being connected to the upper sheet and the bottom of said second chamber being connected to the lower sheet of said air cell, and said second chamber having upper and lower openings which connect said second chamber to the atmosphere, a cable which is firmly attached to the upper sheet of the bladder at said upper opening and which extends through said second chamber, out of said lower opening and connects to a component position indicating apparatus according to the invention, said cable being freely translatable through said lower opening, and inflation means connected to said air cell for varying the pressure within said first chamber, wherein upon inflation of the first chamber, the upper opening of the second chamber moves away from the lower opening, drawing said cable with it, said movement of the cable being detected by the position indicating apparatus.